1. Field of the Invention
The present invention relates generally to digital communications networks and more particularly to methods and apparatus for efficiently counting octets and implementing an octet counting mode in Signaling System No. 7.
2. Description of the Related Art
Digital communications systems have been replacing analog systems for the past several decades. Present communications needs, including cellular telephones and computer networks, rely almost exclusively on digital systems. Signaling System No. 7 ("SS7") is an all digital intelligent network and it provides the networking control for most of this communication. In the 1960s, the Telecommunications Standards Society of the International Telecommunications Union (once known as the CCITT) developed Signaling System No. 6 ("SS6"), which was the predecessor to SS7. The central element of SS7 is that it separates the signaling information from the data. SS7 utilizes a message structure which allows control information to be routed to network nodes independently of the data to which the control information pertains. In the telephone communications industry, this enables call set-up and tear down to be done much faster and without tying up a voice/data line.
One of the first uses for SS7 was to enable switching networks to process 800 numbers. This necessitated retrieving routing information for the 800 number, as well as billing information, from a central database, and SS7 provided this capability. Indeed, this database access capability is used in a variety of telephone services, such as providing information for Caller ID, for verifying credit card numbers and personal identification numbers ("PINs"), and for providing subscriber information amongst different cellular regions to allow Call Roaming.
Many other methods of signaling have been used in the past, including using direct current ("DC") levels, Single Frequency tones above the audible range, current interruption for rotary dialing, and In-Band signaling in the audible range. Each of these had significant limitations which pushed the industry toward an all digital network and which SS7 overcomes.
The current European standard for SS7 is a standard referred to as Q.703. The standard contains all of the specifications that a SS7 provider must meet. One of these involves counting octets (or 8-bit bytes) as they are received and performing a series of functions after a given number, usually 16, of octets have been counted. One such function is to put the system into an octet counting mode if particular error conditions exist.
In a typical application, a digital signal processor ("DSP") is used to interface to the actual transmission medium and to receive and transmit the information. In a system utilizing a DSP, the system designer will typically implement much of the SS7 standard in software which will be downloaded into the DSP. Because the software is resident in the DSP, it is well-suited to the tasks that are generated every 16 octets.
Other implementations of SS7 are not as well-suited to performing these tasks, however. Another popular method of implementing communications devices is to use a serial communications controller, such as a Universal Asynchronous Receiver Transmitter ("UART"). These devices cannot process code (software, firmware, etc.) and must use another processing device, such as a microprocessor or some other intelligent peripheral device or programmable device. This requires the serial communications device to interrupt the processor and this is a time consuming process. In an implementation in which the processor controls multiple communications lines, the processor will be interrupted multiple times every 16 octets. This severely impairs performance. Accordingly, there is a need for a method and system for implementing SS7 which overcome these problems.